Capacitance sensors/sensing systems that respond to charge, current, or voltage can be used to detect position or proximity (or motion or presence or any similar information), and are commonly used as input devices for computers, personal digital assistants (PDAs), media players and recorders, video game players, consumer electronics, cellular phones, payphones, point-of-sale terminals, automatic teller machines, kiosks, and the like. Capacitive sensing techniques are used in applications such as user input buttons, slide controls, scroll rings, scroll strips, and other types of inputs and controls. One type of capacitance sensor used in such applications is the button-type sensor, which can be used to provide information about the proximity or presence of an input. Another type of capacitance sensor used in such applications is the touchpad-type sensor, which can be used to provide information about an input such as the position, motion, and/or similar information along one axis (1-D sensor), two axes (2-D sensor), or more axes. Both the button-type and touchpad-type sensors can also optionally be configured to provide additional information such as some indication of the force, duration, or amount of capacitive coupling associated with the input. Examples of 1-D and 2-D touchpad-type sensor based on capacitive sensing technologies are described in United States Published Application 2004/0252109 A1 to Trent et al. and U.S. Pat. No. 5,880,411, which issued to Gillespie et al. on Mar. 9, 1999. Such 1-D and 2-D sensors can be readily found, for example, in input devices of electronic systems including handheld and notebook-type computers.
A user generally operates a capacitive input device by placing or moving one or more fingers, styli, and/or objects, near the input device an in a sensing region of one or more sensors located on or in the input device. This creates a capacitive effect upon a carrier signal applied to the sensing region that can be detected and correlated to positional information (such as the position(s), proximity, motion(s), and/or similar information) of the stimulus/stimuli with respect to the sensing region. This positional information can in turn be used to select, move, scroll, or manipulate any combination of text, graphics, cursors, highlighters, and/or any other indicator on a display screen. This positional information can also be used to enable the user to interact with an interface, such as to control volume, to adjust brightness, or to achieve any other purpose.
Although capacitance sensors have been widely adopted, sensor designers continue to look for ways to improve the sensors' functionality and effectiveness. In particular, engineers continually strive to reduce the effects of spurious noise on such sensors. Many capacitive sensors, for example, currently include ground planes or other structures that shield the sensing regions from external and internal noise signals. While ground planes and other types of shields held at a roughly constant voltage can effectively prevent some spurious signals from interfering with sensor operation, they can also reduce sensor resolution or increase parasitic effects, such as by increasing parasitic capacitance. Therefore, the performance of such devices is by no means ideal.
Accordingly, it is desirable to provide systems and methods for quickly, effectively and efficiently detecting a measurable capacitance while preventing at least some of the adverse effects that can result from spurious noise signals and/or enhance resolution. Moreover, it is desirable to create a scheme that can be implemented using readily available components, such as standard ICs, microcontrollers, and passive components. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.